.Protists (pronounced /ˈproʊtɨst/) are a diverse group of eukaryoticmicroorganisms.^Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes.

^Clear Turn Off Turn On The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes Your browsing activity is empty.

.Historically, protists were treated as the kingdomProtista but this group is no longer recognized in modern taxonomy.^Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes.

[1].Instead, it is "better regarded as a loose grouping of 30 or 40 disparate phyla with diverse combinations of trophic modes, mechanisms of motility, cell coverings and life cycles."^These taxonomic transfers were based mainly on comparisons of cell structure and details of life cycles.

.The protists do not have much in common besides a relatively simple organization[3] — either they are unicellular, or they are multicellular without specialized tissues.^All are multicellular although without much specialization of cell types.

^The protists are a paraphyletic grade, rather than a natural ( monophyletic ) group, and do not have much in common besides a relatively simple organization (unicellular, or multicellular without highly specialized tissues).

.Because these groups often overlap, they have been replaced by phylogenetic-based classifications.^Almost all of them have chlorophyll A, most have chlorophyll C, but only a few have chlorophyll B. They also have a variety of carotenoids and other pigments, and frequently they are grouped into Divisions based on similarities in pigments.

^All of the characteristics that this group shares are primitive traits, a perilous thing to base any classification on, because convergent evolution may be responsible for these superficial similarities.

.However, they are still useful as informal names for describing the morphology and ecology of protists.^As the early descriptions were based on light microscopical observation, they used to include several protist genera of uncertain affinity, such as Phyllomitus spp.

^The FISH using the group-specific probe also detected the symbionts of the same morphology from almost all the cells of the protist species.

BioMed Central | Full text | Complex coevolutionary history of symbiotic Bacteroidales bacteria of various protists in the gut of termites1 February 2010 3:45 UTCwww.biomedcentral.com [Source type: Academic]

.Protists live in almost any environment that contains liquid water.^Water molds are fungus-like protists that live in moist environments.

.Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton.^In addition, many protists harbour prokaryotes or eukaryotes (such as those that gave rise to secondary and tertiary plastids [ 7 ]) as endosymbionts.

^Even among the photosynthetic protists, different combinations of photopigments, various schemes for storing food, and a variety of reproduction schemes makes it unlikely that many of these are related.

.Other protists, such as the Kinetoplastids and Apicomplexa, are responsible for a range of serious human diseases, such as malaria and sleeping sickness.^Animal-like protists are responsible for diseases such as malaria, amoebic dysentery, toxoplasmosis, African Sleeping Sickness and Giardiasis in humans.

Contents

Classification

Historical classifications

.The first division of the protists from other organisms came in the 1830s, when the German biologist Georg A. Goldfuss introduced the word protozoa to refer to organisms such as ciliates and corals.^Protists belong to the Kingdom Protista, which include mostly unicellular organisms that do not fit into the other kingdoms.

^The amoebae in the Unikont group are more closely related to animals than they are to other so-called amoebae in the other groups, such as...RHIZARIA, a group of mostly amoebae that include the exquisitely beautiful Radiolarians, Foraminiferans (which Haeckel loved and illustrated profusely), various plant parasites, and a whole host of other interesting unicellular creatures.

.The formal taxonomic category Protoctista was first proposed in the early 1860s by John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals.^It does not include Plants, Animals, or Fungi.

.He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants, animals and minerals.^The semiconstrained tree was developed by using the distance tree to define the following subtrees: the spirochetes, the γ- and β-Proteobacteria, the non-Rickettsiales α-Protebacteria and a mitochondrial cpn60 subtree of animals, fungi, and plants.

^Next to the Chromacea come the Bacteria, which have been evolved from them by the remarkable change in nutrition which gives us the simple explanation of the differentiation of plant and animal in the protist kingdom.

[4].The kingdom of minerals was later removed from taxonomy by Ernst Haeckel, leaving plants, animals, and the protists as a “kingdom of primitive forms”.^In many ways fungi are more closely related to animals than to plants , and they have been thought to share a common protist ancestor with animals.

.Herbert Copeland resurrected Hogg's label almost a century later, arguing that "Protoctista" literally meant "first established beings", Copeland complained that Haeckel's term protista included anucleated microbes such as bacteria.^The term was first suggested in 1866 by Ernst Haeckel .

Copeland's use of the term protoctista did not. .In contrast, Copeland's term included nucleatedeukaryotes such as diatoms, green algae and fungi.^Plants , including the green algae ( Chlorophyta ) are described in a separate page.

^In terms of conventional classifications of the lower eukaryotes but considering the system used in this article, the major taxa treated here as protists include the algae , the protozoa, and the so-called lower, or zoosporic (motile), fungi.

[6].This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life.^Kingdom Monera (bacteria and viruses), and the Kingdom Fungi, and also the Kingdom Protista.

[7].The kingdom Protista was later modified to separate prokaryotes into the separate kingdom of Monera, leaving the protists as a group of eukaryotic microorganisms.^Then attempt to group the phyla into kingdoms.

[8].These five kingdoms remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that neither protists or monera were single groups of related organisms (they were not monophyletic groups).^In the Five Kingdom system of classification, all prokaryotes are assigned to the Kingdom Monera.

Modern classifications

.Currently, the term protist is used to refer to unicellular eukaryotes that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues.^They can be either unicellular or multicellular, and in this group we find the first inkling of what is to come in evolutionary history, the union of eukaryotic cells into a colonial organism, where various cell types perform certain tasks, communicate with one another, and together function like a multicellular organism.

^Samuel Arbesman designed the “Milky Way Transit Authority” using only the tube map as a working model… Protozoans Against Intelligent Design — The Journal of Eukaryotic Microbiology has just published a very nice paper showing how the details of protist evolution “dispel the myths of intelligent design.” Generally, protists are “unicellular eukaryotes that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues.” Think amoebae or foraminifera… .

[9].The term protozoa is used to refer to heterotrophic species of protists that do not form filaments.^Most species are multicellular often with interwoven fibers forming filaments, which are delicate and feathering .

^The cells of the protist species that stably harbored Bacteroidales symbionts were physically isolated and used for PCR amplification of bacterial 16S rRNA gene.

BioMed Central | Full text | Complex coevolutionary history of symbiotic Bacteroidales bacteria of various protists in the gut of termites1 February 2010 3:45 UTCwww.biomedcentral.com [Source type: Academic]

.These terms are not used in current taxonomy, and are retained only as convenient ways to refer to these organisms.^We also combined these results with the information from published genomes and mapped the occurrences of the genes onto the current hypothesis of organismal relationships among eukaryotes (Figure 1 ) [ 29 - 31 ].

The taxonomy of protists is still changing. .Newer classifications attempt to present monophyletic groups based on ultrastructure, biochemistry, and genetics.^All of the characteristics that this group shares are primitive traits, a perilous thing to base any classification on, because convergent evolution may be responsible for these superficial similarities.

.Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes.^The tendency was to treat Kingdom Protista as the taxonomic home for all eukaryotes that did not fit comfortably into the definitions of plants, fungi, and animals.

) and instead lists organisms in hierarchical lists. .This is intended to make the classification more stable in the long term and easier to update.^About Us Privacy Policy Terms of Use RSS Feeds E-mail Updates Contact Us Advertise with Us Games MORE...

.In flagellates, for example, filter feeding may sometimes occur where the flagella find the prey.^The polypeptides or derivatives may be used to treat any mammal, for example, human, livestock, pets, to prevent infection from occurring.

.This is then taken into the cell via endocytosis (usually phagocytosis; sometimes pinocytosis).^Most ciliates engulf their food by phagocytosis, a process of surrounding the food with plasma membrane as it is taken into the cell.

.Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually.^Many have very complex life cycles.

[12].However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of Plasmodium in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species.^In fact, sexual reproduction —that is, the union of one male and one female gamete (syngamy)—is the most common sexual phenomenon and occurs quite widely among the protists—for example, among various flagellate and sarcodine groups and among many parasitic phyla ( e.g., in Plasmodium, a malaria-causing organism).

^The probe Bactd-937 for most Bacteroidales members [ 23 ] was used for the initial survey of protist-associated symbionts.

BioMed Central | Full text | Complex coevolutionary history of symbiotic Bacteroidales bacteria of various protists in the gut of termites1 February 2010 3:45 UTCwww.biomedcentral.com [Source type: Academic]

^Next to the Chromacea come the Bacteria, which have been evolved from them by the remarkable change in nutrition which gives us the simple explanation of the differentiation of plant and animal in the protist kingdom.

^The phylogeny of the Bacteroidales symbionts were inferred to understand the relationships to the host protist phylogeny, the connection with their morphology, the extent of their specificity, and the evolutionary process of these impressive symbiotic associations.

BioMed Central | Full text | Complex coevolutionary history of symbiotic Bacteroidales bacteria of various protists in the gut of termites1 February 2010 3:45 UTCwww.biomedcentral.com [Source type: Academic]

^Polypeptides according to the invention may be used to treat fungal and/or protist infections as a monotherapy (i.e.

Definition from Wiktionary, a free dictionary

German

Noun

This German entry was created from the translations listed
at protist. .It may be less
reliable than other entries, and may be missing parts of speech or
additional senses.^The Archaezoa are primitive unicellular eukaryotes; primitive in the sense that they may better resemble the ancestral eukaryote than do less primitive eukaryotes .

Most protists are very small. They are made up of one or a few cells at best – they are microscopic and therefore usually invisible to the naked eye. Some algae are protists, if they are single-celled. Many protists are part of the plankton and are very important for the ecosystem. The cells found in protists may be extremely complex, and are often little understood. It is now possible to do DNA sequencing, and a number of protists have been analysed. The results show that the Protista is not a monophyletic group. It is paraphyletic, and not a single clade. The taxonomy of the Protista is therefore rather confused.

An example of a single celled organism in the protist kingdom is the Paramecium or "slipper animalcule." The Paramecium moves using its small, hair-like fibers called cilia, and eats using the cilia to sweep the food into its food vacuole. Other protists can be amoebas, which move by extending pseudopods and flowing into them, or flowing around food particles and engulfing them.

Origin and taxonomy

Protists are not a monophyleticclade. The term is a convenient holdall for about 20 different kinds of single-celle eukaryotes. They differ in their cell organelles, specialised units which carry out well-defined functions, like mitochondria and plastids. This proves they have made the transition from prokaryotes in different ways. It is fairly clear now that all or most of these organelles have their origin in once-independent prokaryotes (bacteria or archaea), and that the eukaryote cell is a 'community of micro-organisms' working together in 'a marriage of convenience'.[1][2][3][4] Admittedly, the Protista is a collection of disparate single-celled forms, but while a more sophisticated taxonomy is in flux (changing), Protista is still a useful term.

References

↑ Margulis L. Schwartz K.V. & Dolan M. 1999. Diversity of life: the illustrated guide to the five kingdoms. Jones & Bartlett, Boston, p94. In this work the authors propose 19 phyla for the Protista, and call this 'Kingdom' the 'Protoctista', a term which is unfortunately almost unpronounceable.